My (slightly biased) suggestion:
Pros: Excellent temperament with other dogs, children and people. They are the guy at the party with the lamp shade on his head. Portable.
Cons: Tend to gain weight (making them less portable), champion snorers (but that's charming, right?) Overheats easily.
and the runners up...
I'm going to ahead and throw this out there, verbatim....
(1.) MIXED BREED
Pros: You’re saving a life. And a mutt’s diverse genes often mean he’ll have a more middle-of-the-road temperament.
Cons: Without knowing the dog’s lineage, it’s hard to foresee health problems.
Pros: One of the hot breeds this season, these are playful, happy dogs.
Cons: Lot of grooming unless you shave them down, and recent litters appearing in city pet stores are showing “fear issues,” according to one trainer.
Pros: Portable, clever, and tenacious. The Napoleons of the sidewalk.
Cons: They can be aggressive and very barky. Spine troubles.
Pros: Soft, curly coat. Playful temperament. The season’s hot crossbreed.
Cons: Almost all Shih-Poos come from pet stores (good breeders generally don’t breed crosses), so you won’t have much assurance about its stock.
(5.) CAVALIER KING CHARLES SPANIEL
Pros: Friendly, joyful, and great with children—the golden retriever of small-breed dogs.
Cons: Cavaliers need active exercise (they love playing fetch), they are predisposed to heart problems, and they shed.
(6.) NORFOLK TERRIER
Pros: Hardy, fun dogs with easygoing temperaments. Grooming’s not excessive.
Cons: The Norfolk’s wiry coat may discourage some from snuggling.
(7.) PORTUGUESE WATER DOG
Pros: Smaller than a standard poodle and very fun. Clownish, hardy, excellent for families with kids.
Cons: The “clowning” that’s so cute when he’s a puppy can become out-of-control behavior without strict training.
(8.) FRENCH BULLDOG
Pros: Good, balanced temperament and not too energetic.
Cons: Thanks to that cute pushed-in face, respiratory problems can be an issue.
Pros: The gentle giant of big dogs. Quiet and calm, greyhounds love to hang out.
Cons: That low energy, plus the “sad” look.
(10.) LABRADOR RETRIEVER
Pros: One of the most common city dogs. High energy level, ebullient, athletic.
Cons: Big shedders, and if they’re not trained, they can go a little stir crazy.
Other useful links...
Getting around the city....if your dog isn't subway friendly...and the cabs are passing you...
For treats, I'd suggest Trader Joe's. They have the best prices and are health conscious. The Brooklyn location is now open (take the 2/3 train, it's located on Court St)...it's larger and less crowded than the Union Square location.
When you dog is fully vaccinated (and comfortable with other furry friends) there are several dog runs in the city. Check out the locations here.